Multi-speed gearbox

ABSTRACT

Multi-stage transmission comprises four planetary gear sets, rotatable shafts and six shift elements. Sun of first set is connected to fifth shaft which is connectable, via first clutch, to drive shaft and is couplable, via third brake, to housing. Drive shaft is connectable, via second clutch, to seventh shaft which is connectable to carrier of fourth set and ring of third set and is connectable, via third clutch, to eighth shaft which is connected to sun of second. Sixth shaft is connected to ring of first set, carrier of second set and ring of fourth set. Third shaft is connected to sun of third set and sun of fourth set and can be coupled, via first brake, to housing. Fourth shaft is connected to carrier of first set and ring of second set and is couplable, via second brake, to housing. Drive shaft is connected to carrier of third set.

This application is a National Stage completion of PCT/EP2013/055077filed Mar. 13, 2013, which claims priority from German patentapplication serial no. 10 2012 206 809.0 filed Apr. 25, 2012.

FIELD OF THE INVENTION

The present invention relates to a multi-stage transmission of aplanetary design, in particular an automatic transmission for a motorvehicle.

BACKGROUND OF THE INVENTION

According to the prior art, automatic transmissions, particularly formotor vehicles, comprise planetary gear sets that are shifted usingfriction elements or shift elements such as clutches and brakes, andtypically are connected to a start-up element, such as a hydrodynamictorque converter or a fluid coupling, that is subject to a slip effectand is provided optionally with a lock-up clutch.

Such an automatic transmission is known, for example, from DE 199 12 480B4 by the applicant. It comprises three single-carrier planetary gearsets, as well as three brakes and two clutches for shifting six forwardgears and one reverse gear, an input shaft and an output shaft, whereinthe carrier for the first planetary gear set is permanently connected tothe ring gear of the second planetary gear set, and the carrier for thesecond planetary gear set is permanently connected to the ring gear ofthe third planetary gear set, and the input shaft is directly connectedto the sun gear of the second planetary gear set.

Furthermore, in the known transmission, the input shaft is connectable,by means of the first clutch, to the sun gear of the first planetarygear set, and by means of the second clutch to the carrier of the firstplanetary gear set, wherein the sun gear of the first planetary gear setis connectable, by means of the first brake, to a housing of thetransmission, and the carrier of the first planetary gear set isconnectable, by means of the second brake, to the housing of thetransmission, wherein the sun gear of the third planetary gear set isconnectable, by means of the third brake, to the housing of thetransmission. The output shaft of the transmission is permanentlyconnected to the carrier for the third planetary gear set and the ringgear of the first planetary gear set.

Furthermore, a nine-speed multi-stage transmission is known from DE 2936 969 A1; it comprises eight shift elements and four planetary gearsets, wherein one planetary gear set serves as a front-mountedtransmission and the main gearing includes a Simpson set and a furtherplanetary gear set serving as a reverse gearing.

Further multi-stage transmissions are known, for example, from theapplicant's DE 10 2005 010 210 A1 and DE 10 2006 006 637 A1.

Automatically shiftable vehicle transmissions of a planetary design arealready generally described numerous times in the prior art and arecontinually undergoing further development and improvement. Thesetransmissions should have a relatively simple design, in particularrequiring a small number of shift elements, and minimize the need fordouble shifting, i.e., engaging and/or disengaging two shift elements,when sequential shifting is performed, thereby ensuring that only oneshift element is ever switched when shifting is performed in definedgroups of gears.

The applicant's document, DE 10 2008 000 428 A1, discloses a multi-stagetransmission of a planetary design that includes an input drive and anoutput drive which are disposed in a housing. In the known transmission,at least four planetary gear sets, referred to in the following as thefirst, second, third and fourth planetary gear sets, at least eightrotatable shafts, referred to in the following as the drive shaft,output shaft, third, fourth, fifth, sixth, seventh and eighth shafts, aswell as at least six shift elements, comprising brakes and clutches, areprovided, the selective engagement of which produces differenttransmission ratios between the input drive and the output drive so thatpreferably nine forward gears and a reverse gear can be implemented.

The first and second planetary gear sets, which are preferably designedas minus planetary gear sets, thus having a negative stationarytransmission ratio, form a shiftable front-mounted gear set, wherein thethird and fourth planetary gear sets form a main gear set.

In the known multi-stage transmission, the carriers of the first andsecond planetary gear sets are coupled together via the fourth shaft,which is connected to an element of the main gear set, the ring gear ofthe first planetary gear set is coupled to the sun gear of the secondplanetary gear set via the eighth shaft, which is detachably connectableto the drive shaft, via a first clutch, and the sun gear of the firstplanetary gear set can be coupled to a housing of the transmission bymeans of the third shaft, via a first brake, and is detachablyconnectable to the drive shaft, via a second clutch, wherein the ringgear of the second planetary gear set can be coupled to a housing of thetransmission by means of the fifth shaft, via a second brake. Inaddition, the seventh shaft is permanently connected to at least oneelement of the main gear set, and can be coupled to the housing of thetransmission, via a third brake, wherein the sixth shaft is permanentlyconnected to at least one further element of the main gear set and isdetachably connectable to the drive shaft, via a third clutch; theoutput shaft is permanently connected at least to one further element ofthe main gear set.

In the known transmission, the fourth shaft is preferably permanentlyconnected to the ring gear of the third planetary gear set, the sixthshaft is permanently connected to the ring gear of the fourth planetarygear set and to the carrier of the third planetary gear set, and isdetachably connectable to the drive shaft, via the third clutch.Furthermore, the seventh shaft is permanently connected to the sun gearsof the third and fourth planetary gear sets, and can be coupled to ahousing of the transmission, via the third brake. In this case, theoutput drive is produced via the output shaft that is permanentlyconnected to the carrier of the fourth planetary gear set. Furthermore,the third and fourth planetary gear sets can be combined or reduced to aRavigneaux set having a common carrier and a common ring gear.

According to the prior art, the shift elements of the multi-stagetransmission thus designed, which are usually designed as lamellarclutches or brakes, are actuated hydraulically, which disadvantageouslyresults in significant hydraulic losses. In order to avoid theseactuation losses, the use of need-based, actuatable shift elements wouldbe especially advantageous.

Need-based shift elements may be understood, in particular, to be shiftelements in which no energy or less energy is needed to maintain theshift state than is needed to switch the shift state.

In order to make it possible to use shift elements that can be actuatedupon demand, the shift elements, in particular the clutches, should beeasily accessible from outside.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a multi-stagetransmission of the initially described type, which has nine forwardgears and a reverse gear, having a sufficient transmission ratio, inwhich the design complexity, the component load and the installationsize are optimized, and in which the efficiency is improved. Moreover,the shift elements of the transmission should be easily accessible fromoutside, as a result of which the installation of shift elements thatcan be actuated upon demand is made possible. In addition, thetransmission should be suitable for standard design and for a transversefrontal design.

Accordingly, a multi-stage transmission, according to the invention, ofa planetary design is proposed which has an input shaft and an outputshaft which are disposed in a housing. In addition, there are providedat least four planetary gear sets which are designated, in thefollowing, as the first, second, third, and fourth planetary gear sets,eight rotatable shafts which are designated, in the following, as thedrive shaft, output shaft, third, fourth, fifth, sixth, seventh, andeighth shafts, and six shift elements, preferably designed as lamellarshift elements or as a form locking shift element, comprising brakes andclutches, whose selective engagement produces different transmissionratios between the drive shaft and the output shaft and, therefore,preferably nine forward gears and one reverse gear can be implemented.

The planetary gear sets of the transmission are preferably designed asminus planetary gear sets.

As is well known, a simple minus planetary gear set comprises a sungear, a ring gear, and a carrier on which the planetary gears arerotatably supported, the planetary gears meshing with the sun gear andthe ring gear. As a result, when the carrier is fixed, the ring gear hasa direction of rotation that is opposite that of the sun gear. Incontrast, a simple plus planetary gear set comprises a sun gear, a ringgear and a carrier, on which inner and outer planet gears are rotatablycarried, wherein all inner planet gears mesh with the sun gear and allouter planet gears mesh with the ring gear, and each inner planet gearmeshes with only one outer planet gear. As a result, when the carrier isfixed, the ring gear has the same direction of rotation as the sun gear,and a positive stationary transmission ratio results.

According to the invention, the sun gear of the first planetary gear setis connected to the fifth shaft which can be detachably connected, via afirst clutch, to the drive shaft, and which can be coupled, via a thirdbrake, to the housing, wherein the drive shaft can be detachablyconnected, via a second clutch, to the seventh shaft, which is connectedto the carrier of the fourth planetary gear set and the ring gear of thethird planetary gear set, and can be detachably connected, via a thirdclutch, to the eighth shaft, which is connected to the sun gear of thesecond planetary gear set.

In addition, the sixth shaft is connected to the ring gear of the firstplanetary gear set, the carrier of the second planetary gear set and tothe ring gear of the fourth planetary gear set, wherein the third shaftis connected to the sun gear of the third planetary gear set and the sungear of the fourth planetary gear set, and can be coupled, via a firstbrake, to the housing.

In addition, the fourth shaft is connected to the carrier of the firstplanetary gear set and the ring gear of the second planetary gear setand can be coupled, via a second brake, to the housing, wherein theoutput shaft of the transmission is connected to the carrier of thethird planetary gear set.

Because the first, second and third clutches are disposed on the driveshaft of the transmission and the remaining shift elements are designedas brakes, good accessibility of all the shift elements of thetransmission is ensured, as a result of which the shift elements may bedesigned as shift elements that can be actuated upon demand. Within thecontext of further embodiments, shift elements of the transmission maybe designed, inter alia, as shift elements that can be hydraulicallyactuated.

In addition, transmission ratios are attained that are especiallysuitable for passenger vehicles, as well as a greater overall gear ratioof the multi-stage transmission, which results in improved drivingcomfort and a significant reduction in fuel consumption.

Furthermore, design complexity is significantly reduced with themulti-stage transmission according to the invention due to a low numberof shift elements. Using the multi-stage transmission according to theinvention, it is advantageously possible to perform a start-up using ahydrodynamic converter, an external start-up clutch, or any othersuitable external start-up element. It is also conceivable to perform astart-up using a start-up element integrated in the transmission.Preferably, a shift element that is actuated in the first forward gearand in the reverse gear is suitable for this.

Moreover, the multi-stage transmission, according to the invention,results in good efficiency in the main drive gears with respect to draglosses and gearing losses.

Low torques are advantageously present in the shift elements and in theplanetary gear sets of the multi-stage transmission, therebyadvantageously reducing wear in the multi-stage transmission. Inaddition, the low torques make it possible to utilize correspondinglylow dimensions, thereby reducing the necessary installation space andrelated costs. Furthermore, the rotational speeds of the shafts, shiftelements, and planetary gear sets are low.

In addition, the transmission, according to the invention, is designedto allow adaptability to different drive train embodiments, both interms of power flow direction and spatial aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail in the following, as anexample, with reference to the attached Figures. They show:

FIG. 1: a schematic view of a preferred embodiment of a multi-stagetransmission according to the invention; and

FIG. 2: an example of a shift pattern for a multi-stage transmissionaccording to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a multi-stage transmission, according to the invention,which has a drive shaft 1, an output shaft 2, and four planetary gearsets P1, P2, P3 and P4, which are disposed in a housing G. In theexample shown in FIG. 1, planetary gear sets P1, P2, P3 P4 are designedas minus planetary gear sets. According to the invention, at least oneof the planetary gear sets P1, P2, P3, P4 can be implemented as a plusplanetary gear set if the carrier and ring gear connection are exchangedand, simultaneously, the value of the stationary transmission ratio isincreased by 1 in comparison to the embodiment as a minus planetary gearset.

In the embodiment shown here, viewed axially, the planetary gear setsP1, P2, P3, P4 are disposed in the sequence of the first planetary gearset P1, the second planetary gear set P2, the third planetary gear setP3, the fourth planetary gear set P4. According to the invention, theaxial sequence of the individual planetary gear sets and theconfiguration of the shift elements may be freely selected as long asthis allows the elements to connect.

As shown in FIG. 1, six shift elements are provided, namely, threebrakes, 03, 04, 05 and three clutches 15, 17, 18. The spatialdisposition of the shift elements can be arbitrary, and is limited onlyby the dimensions and the exterior design shape. The clutches and thebrakes of the transmission are preferably designed as friction elementsor lamellar shift elements respectively, however, they also may bedesigned as form-locking shift elements.

Selective shifting of nine forward gears and one reverse gear can beimplemented using these shift elements. The multi-stage transmission,according to the invention, has a total of eight rotatable shafts,namely, the shafts 1, 2, 3, 4, 5, 6, 7 and 8, wherein the drive shaftforms the first shaft, and the output shaft forms the second shaft ofthe transmission.

According to the invention, in a multi-stage transmission according toFIG. 1, it is provided that the sun gear of the first planetary gear setP1 is connected to the fifth shaft 5, which can be detachably connected,via a first clutch 15, to the drive shaft 1 and can be coupled, via athird brake 05, to the housing G, wherein the drive shaft 1 can bedetachably connected, via a second clutch 17, to the seventh shaft 7,which is connected to the carrier of the fourth planetary gear set P4and the ring gear of the third planetary gear set P3, and can bedetachably connected, via a third clutch 18, to the eighth shaft 8,which is connected to the sun gear of the second planetary gear set P2.

As is evident from FIG. 1, the sixth shaft 6 is connected to the ringgear of the first planetary gear set P1, the carrier of the secondplanetary gear set P2 and the ring gear of the fourth planetary gear setP4, wherein the third shaft 3 is connected to the sun gear of the thirdplanetary gear set P3 and the sun gear of the fourth planetary gear setP4 and can be coupled, via a first brake 03, to the housing G.

In addition, the fourth shaft 4 is connected to the carrier of the firstplanetary gear set P1 and the ring gear of the second planetary gear setP2 and can be coupled, via a second brake 04, to the housing G, whereinthe output shaft 2 of the transmission is connected to the carrier ofthe third planetary gear set P3.

In connection herewith, viewed axially, the first, second and thirdclutches 15, 17, 18 may be disposed side by side and may be designed aslamellar shift elements and have a common external disk carrier. In theembodiment shown, the first brake 03 and the third clutch 18, inparticular, are suited for design as a dog clutch element, whichsignificantly improves fuel consumption.

FIG. 2 shows an example of a shift pattern of a multi-stage transmissionaccording to FIG. 1. Three shift elements are engaged for every gear.The shift pattern shows, as examples, the particular transmission ratiosi of the individual gear steps and, to be determined therefrom, the gearincrements or step changes φ to the next higher gear, wherein the value9.016 is the transmission ratio spread.

In the example shown, the values for the stationary transmission ratiosof the planetary gear sets P1, P2, P3, P4, implemented as minusplanetary gear sets, are −2.366, −1.600, −3.189 and −2.763,respectively, FIG. 2 shows that only one shift element must be engagedand one shift element must be disengaged when sequentially shifting,since two neighboring gear steps jointly use two shift elements. It isalso shown that a large transmission ratio spread is attained with smallgear increments.

The first forward gear is attained by engaging the first and secondbrakes 03, 04 and the third clutch 18, the second forward gear isattained by engaging the first and third brakes 03, 05 and the thirdclutch 18, the third forward gear is attained by engaging the firstbrake 03 and the first and third clutches 15, 18, the fourth forwardgear is attained by engaging the first brake 03 and the second and thirdclutches 17, 18, the fifth forward gear, which is designed as a directgear in the example shown, is attained by engaging the first, second andthird clutches 15, 17, 18, the sixth forward gear is attained byengaging the third brake 05 and the second and third clutches 17, 18,the seventh forward gear is attained by engaging the second brake 04 andthe second and third clutches 17, 18, the eighth forward gear isattained by engaging the second and third brakes 04, 05 and the secondclutch 17, and the ninth forward gear is attained by engaging the secondbrake 04 and the first and second clutches 15, 17, wherein the reversegear is attained by engaging the first and second brakes 03, 04 and thefirst clutch 15.

Alternatively, the fourth forward gear may be shifted by means ofadditional shift combinations, which are designated as M in FIG. 2.Accordingly, the fourth forward gear can be attained by engaging thefirst and second brakes 03, 04 and the second clutch 17, or by engagingthe first brake 03 and the first and second clutches 15, 17, or byengaging the first and third brakes 03, 05 and the second clutch 17.

Since the first and second brakes 03, 04 and the first and thirdclutches 15, 18 are engaged in the first forward gear and/or in thereverse gear, these shift elements can be used as start-up elements.

According to the invention, different gear increments also result fromthe same shift pattern depending on the shift logic, thereby making itpossible to implement an application-specific or a vehicle-specificvariation.

According to the invention, it is also optionally possible to provideadditional freewheels at each suitable location of the multi-stagedtransmission, for example, between a shaft and the housing, or possiblyto connect two shafts.

An axle differential and/or a distributor differential can be disposedon the drive side or on the output side.

Within the scope of an advantageous development of the invention, thedrive shaft 1 can be separated from a drive motor, as needed, by aclutch element, wherein a hydrodynamic converter, a hydraulic clutch, adry start-up clutch, a wet start-up clutch, a magnetic powder clutch, acentrifugal clutch or the like can be used as the clutch element. It isalso possible to dispose such a start-up element in the power flowdirection after the transmission wherein, in this case, the drive shaft1 is permanently connected to the crankshaft of the drive motor.

The multi-stage transmission, according to the invention, also makes itpossible to situate a torsional-vibration damper between the drive motorand the transmission.

Within the scope of a further, not depicted embodiment of the invention,a wear-free brake, for instance, a hydraulic or electric retarder or thelike, can be disposed on each shaft, preferably on the drive shaft 1 orthe output shaft 2 which is, in particular, of special significance foruse in commercial vehicles. Furthermore, a power take-off drive can beprovided on each shaft, preferably on the input shaft 1 or the outputshaft 2, for driving additional assemblies.

The friction shift elements that are used can be designed as powershiftable clutches or brakes. In particular, force locking clutches orbrakes, for instance lamellar clutches, band brakes, and/or coneclutches, can be used.

A further advantage of the multi-stage transmission presented here isthat an electric machine can be attached to each shaft as a generatorand/or as an additional drive machine.

REFERENCE CHARACTERS

-   1 first shaft, drive shaft-   2 second shaft, output shaft-   3 third shaft-   4 fourth shaft-   5 fifth shaft-   6 sixth shaft-   7 seventh shaft-   8 eighth shaft-   03 first brake-   04 second brake-   05 third brake-   15 first clutch-   17 second clutch-   18 third clutch-   G housing-   P1 first planetary gear set-   P2 second planetary gear set-   P3 third planetary gear set-   P4 fourth planetary gear set-   i transmission ratio-   φ step change

1-7. (canceled)
 8. A multi-stage transmission of a planetary designcomprising: a drive shaft (1), an output shaft (2), first, second, thirdand fourth planetary gear sets (P1, P2, P3, P4) which are disposed in ahousing (G), third, fourth, fifth, six, seventh and eighth rotatableshafts (3, 4, 5, 6, 7, 8), and six shift elements (03, 04, 05, 15, 17,18) comprising brakes (03, 04, 05) and clutches (15, 17, 18) whoseselective engagement produces different transmission ratios between thedrive shaft (1) and the output shaft (2) so that nine forward gears anda reverse gear can be implemented, wherein the sun gear of the firstplanetary gear set (P1) is connected to the fifth shaft (5), and thefifth shaft (5) can be detachably connected, via a first clutch (15), tothe drive shaft (1), and the fifth shaft (5) can be coupled, via a thirdbrake (05), to the housing (G), the drive shaft (1) can be detachablyconnected, via a second clutch (17), to the seventh shaft (7), theseventh shaft (7) is connected to both the carrier of the fourthplanetary gear set (P4) and the ring gear of the third planetary gearset (P3) and the seventh shaft (7) can be detachably connected, via athird clutch (18), to the eighth shaft (8), and the eighth shaft (8) isconnected to the sun gear of the second planetary gear set (P2), thesixth shaft (6) is connected to the ring gear of the first planetarygear set (P1), the carrier of the second planetary gear set (P2) and thering gear of the fourth planetary gear set (P4), the third shaft (3) isconnected to both the sun gear of the third planetary gear set (P3) andthe sun gear of the fourth planetary gear set (P4) and the third shaft(3) can be coupled, via a first brake (03), to the housing (G), thefourth shaft (4) is connected to both the carrier of the first planetarygear set (P1) and the ring gear of the second planetary gear set (P2)and the fourth shaft (4) can be coupled, via a second brake (04), to thehousing (G), and the drive shaft (2) is connected to the carrier of thethird planetary gear set (P3).
 9. The multi-stage transmission accordingto claim 8, wherein the first, the second, the third and the fourthplanetary gear set (P1, P2, P3, P4) are designed as minus planetary gearsets.
 10. The multi-stage transmission according to claim 8, wherein,when viewed axially, the planetary gear sets are disposed in thesequence of the first planetary gear set (P1), the second planetary gearset (P2), the third planetary gear set (P3), the fourth planetary gearset (P4).
 11. The multi-stage transmission according to claim 8, whereinthe shift elements (03, 04, 05, 15, 17, 18) of the transmission aredesigned as shift elements that can be actuated upon demand.
 12. Themulti-stage transmission according to claim 8, wherein at least one ofthe first brake (03) and the third clutch (18) is designed as aform-locking shift element.
 13. The multi-stage transmission accordingto claim 8, wherein a first forward gear is attained by engaging thefirst and the second brakes (03, 04) and the third clutch (18), a secondforward gear is attained by engaging the first and the third brakes (03,05) and the third clutch (18), a third forward gear is attained byengaging the first brake (03) and the first and the third clutches (15,18), a fourth forward gear is attained by engaging the first brake (03)and the second and the third clutches (17, 18), a fifth forward gear isattained by engaging the first, the second and the third clutches (15,17, 18), a sixth forward gear is attained by engaging the third brake(05) and the second and the third clutches (17, 18), a seventh forwardgear is attained by engaging the second brake (04) and the second andthe third clutches (17, 18), an eighth forward gear is attained byengaging the second and the third brakes (04, 05) and the second clutch(17), a ninth forward gear is attained by engaging the second brake (04)and the first and the second clutches (15, 17), and the reverse gear isattained by engaging the first and the second brakes (03, 04) and thefirst clutch (15).
 14. The multi-stage transmission according to claim8, wherein a first forward gear is attained by engaging the first andthe second brakes (03, 04) and the third clutch (18), a second forwardgear is attained by engaging the first and the third brakes (03, 05) andthe third clutch (18), a third forward gear is attained by engaging thefirst brake (03) and the first and the third clutches (15, 18), a fourthforward gear is attained by engaging the first and the second brakes(03, 04) and the second clutch (17), a fifth forward gear is attained byengaging the first, the second and the third clutches (15, 17, 18), asixth forward gear is attained by engaging the third brake (05) and thesecond and the third clutches (17, 18), a seventh forward gear isattained by engaging the second brake (04) and the second and the thirdclutches (17, 18), an eighth forward gear is attained by engaging thesecond and the third brakes (04, 05) and the second clutch (17), a ninthforward gear is attained by engaging the second brake (04) and the firstand the second clutches (15, 17), and the reverse gear is attained byengaging the first and the second brakes (03, 04) and the first clutch(15).
 15. The multi-stage transmission according to claim 8, wherein afirst forward gear is attained by engaging the first and the secondbrakes (03, 04) and the third clutch (18), a second forward gear isattained by engaging the first and the third brakes (03, 05) and thethird clutch (18), a third forward gear is attained by engaging thefirst brake (03) and the first and the third clutches (15, 18), a fourthforward gear is attained by engaging the first brake (03) and the firstand the second clutches (15, 17), a fifth forward gear is attained byengaging the first, the second and the third clutches (15, 17, 18), asixth forward gear is attained by engaging the third brake (05) and thesecond and the third clutches (17, 18), a seventh forward gear isattained by engaging the second brake (04) and the second and the thirdclutches (17, 18), an eighth forward gear is attained by engaging thesecond and the third brakes (04, 05) and the second clutch (17), a ninthforward gear is attained by engaging the second brake (04) and the firstand the second clutches (15, 17), and the reverse gear is attained byengaging the first and the second brakes (03, 04) and the first clutch(15).
 16. The multi-stage transmission according to claim 8, wherein afirst forward gear is attained by engaging the first and the secondbrakes (03, 04) and the third clutch (18), a second forward gear isattained by engaging the first and the third brakes (03, 05) and thethird clutch (18), a third forward gear is attained by engaging thefirst brake (03) and the first and the third clutches (15, 18), a fourthforward gear is attained by engaging the first and the third brakes (03,05) and the second clutch (17), a fifth forward gear is attained byengaging the first, the second and the third clutches (15, 17, 18), asixth forward gear is attained by engaging the third brake (05) and thesecond and the third clutches (17, 18), a seventh forward gear isattained by engaging the second brake (04) and the second and the thirdclutches (17, 18), an eighth forward gear is attained by engaging thesecond and the third brakes (04, 05) and the second clutch (17), a ninthforward gear is attained by engaging the second brake (04) and the firstand the second clutches (15, 17), and the reverse gear is attained byengaging the first and the second brakes (03, 04) and the first clutch(15).
 17. The multi-stage transmission according to claim 8, wherein themulti-stage transmission is an automatic transmission for a motorvehicle.
 18. A multi-stage transmission of a planetary designcomprising: a drive shaft, an output shaft, first, second, third andfourth planetary gear sets which are disposed in a housing, third,fourth, fifth, six, seventh and eighth rotatable shafts, and six shiftelements comprising brakes and clutches whose selective engagementproduces different transmission ratios between the drive shaft and theoutput shaft so that nine forward gears and a reverse gear can beimplemented, wherein the sun gear of the first planetary gear set isconnected to the fifth shaft, and the fifth shaft can be detachablyconnected, via a first clutch, to the drive shaft, and the fifth shaftcan be coupled, via a third brake, to the housing, the drive shaft canbe detachably connected, via a second clutch, to the seventh shaft, theseventh shaft is connected to both the carrier of the fourth planetarygear set and the ring gear of the third planetary gear set and theseventh shaft can be detachably connected, via a third clutch, to theeighth shaft, and the eighth shaft is connected to the sun gear of thesecond planetary gear set, the sixth shaft is connected to the ring gearof the first planetary gear set, the carrier of the second planetarygear set and the ring gear of the fourth planetary gear set, the thirdshaft is connected to both the sun gear of the third planetary gear setand the sun gear of the fourth planetary gear set and the third shaftcan be coupled, via a first brake, to the housing, the fourth shaft isconnected to both the carrier of the first planetary gear set and thering gear of the second planetary gear set and the fourth shaft can becoupled, via a second brake, to the housing, and the drive shaft isdirectly connected to the carrier of the third planetary gear set. 19.The multi-stage transmission according to claim 18, wherein a firstforward gear is attained by engaging the first and the second brakes andthe third clutch, a second forward gear is attained by engaging thefirst and the third brakes and the third clutch, a third forward gear isattained by engaging the first brake and the first and the thirdclutches, a fourth forward gear is attained by engaging the first brakeand the second and the third clutches, a fifth forward gear is attainedby engaging the first, the second and the third clutches, a sixthforward gear is attained by engaging the third brake and the second andthe third clutches, a seventh forward gear is attained by engaging thesecond brake and the second and the third clutches, an eighth forwardgear is attained by engaging the second and the third brakes and thesecond clutch, a ninth forward gear is attained by engaging the secondbrake and the first and the second clutches, and the reverse gear isattained by engaging the first and the second brakes and the firstclutch.
 20. The mufti-stage transmission according to claim 18, whereina first forward gear is attained by engaging the first and the secondbrakes and the third clutch, a second forward gear is attained byengaging the first and the third brakes and the third clutch, a thirdforward gear is attained by engaging the first brake and the first andthe third clutches, a fourth forward gear is attained by engaging thefirst and the second brakes and the second clutch, a fifth forward gearis attained by engaging the first, the second and the third clutches, asixth forward gear is attained by engaging the third brake and thesecond and the third clutches, a seventh forward gear is attained byengaging the second brake and the second and the third clutches, aneighth forward gear is attained by engaging the second and the thirdbrakes and the second clutch, a ninth forward gear is attained byengaging the second brake and the first and the second clutches, and thereverse gear is attained by engaging the first and the second brakes andthe first clutch.
 21. The multi-stage transmission according to claim18, wherein a first forward gear is attained by engaging the first andthe second brakes and the third clutch, a second forward gear isattained by engaging the first and the third brakes and the thirdclutch, a third forward gear is attained by engaging the first brake andthe first and the third clutches, a fourth forward gear is attained byengaging the first brake and the first and the second clutches, a fifthforward gear is attained by engaging the first, the second and the thirdclutches, a sixth forward gear is attained by engaging the third brakeand the second and the third clutches, a seventh forward gear isattained by engaging the second brake and the second and the thirdclutches, an eighth forward gear is attained by engaging the second andthe third brakes and the second clutch, a ninth forward gear is attainedby engaging the second brake and the first and the second clutches, andthe reverse gear is attained by engaging the first and the second brakesand the first clutch.
 22. The multi-stage transmission according toclaim 18, wherein a first forward gear is attained by engaging the firstand the second brakes and the third clutch, a second forward gear isattained by engaging the first and the third brakes and the thirdclutch, a third forward gear is attained by engaging the first brake andthe first and the third clutches, a fourth forward gear is attained byengaging the first and the third brakes and the second clutch, a fifthforward gear is attained by engaging the first, the second and the thirdclutches, a sixth forward gear is attained by engaging the third brakeand the second and the third clutches, a seventh forward gear isattained by engaging the second brake and the second and the thirdclutches, an eighth forward gear is attained by engaging the second andthe third brakes and the second clutch, a ninth forward gear is attainedby engaging the second brake and the first and the second clutches, andthe reverse gear is attained by engaging the first and the second brakesand the first clutch.
 23. The multi-stage transmission according toclaim 18, wherein the multi-stage transmission is an automatictransmission for a motor vehicle.